The strong relationship between posttraumatic stress disorder (PTSD) and interpersonal problems is well documented. PTSD is highly associated with relationship discord, increased intimate partner violence, and difficulties in connecting with others, leading to social isolation. These types of conflicts, as well as the social withdrawal that is common among Veterans with PTSD, diminish the Veteran's opportunities for interaction with supportive others, and serve as a barrier to successful posttraumatic adjustment. Treatments that have been rolled out nationally in VAMCs, e.g., Prolonged Exposure, Cognitive Processing Therapy, and Trauma- Focused CBT, do not directly target these relationship difficulties. Furthermore, data show that only a limited number of Veterans has fully engaged with these interventions. Evidence-based interventions of couples therapy are available, but are not logistically feasible for many couples and do not address the problems of those who are socially isolated. This application proposes a randomized clinical trial of Interpersonal Psychotherapy (IPT-PTSD) as a treatment for Veterans with PTSD and relationship problems. Pilot data suggest that this type of treatment may provide a useful alternative strategy for Veterans who would prefer an individual, relationship-focused approach. We propose comparing IPT-PTSD with Prolonged Exposure (PE), an evidence based treatment for PTSD used in the VHA system. We hypothesize that IPT-PTSD will be statistically equivalent to PE in reducing PTSD symptom severity, and superior to PE in improving interpersonal functioning. IPT-PTSD is also hypothesized to be more effective than PE in improving social adjustment and quality of life. Exploratory analyses will examine whether IPT-PTSD is more effective than PE in reducing suicidal ideation, and will examine hypothesized mediators of improvement in PTSD symptoms in IPT-PTSD.